The existence of an energy gap around the Fermi energy is established experimentally for the intermetallic compound FeGa3. Fe-57 Mossbauer spectra measured at room temperature confirmed the absence of magnetic ordering. The temperature dependence of magnetic susceptibility, chi(T), measured on single-crystalline samples showed diamagnetic behavior below room temperature, and it increased exponentially with temperature above 500 K. Fitting to the high-temperature data yielded an energy gap A of 0.29-0.45 eV. Valence-band x-ray photoemission spectra directly revealed the energy gap, the size of which was estimated to be Delta < (similar to)under tilde> 0.8 eV. These results agree with the prediction by recent band calculations.